Transformer termination for metal-enclosed, compressed-gas-insulated electrical conductors

ABSTRACT

The grounded enclosure tube of the compressed-gas-insulated electrical conductor is attached to the metal wall of a power transformer tank and the energized conductor tube extends into the interior of the transformer tank wherein it is supported and insulated from the tank wall to provide a simple and inexpensive connection between metal enclosed switchgear, for example, and power transformers in a high-voltage electrical substation.

United States Patent Graybill I [54] TRANSFORMER TERMINATION FORMETAL-ENCLOSED, COMPRESSED- GAS-INSULATED ELECTRICAL CONDUCTORS [72]Inventor: Howard W. Graybill, Greensburg, Pa.

{73] Assignee: l-T-E Imperial Corporation, Philadelphia,

[22] Filed: Apr. 24, 1970 [21] Appl.No.: 31,590

{52] US. Cl. ..l74/l8, 174/31 R, 174/142, l74/DIG. 10 [51] Int. Cl...H0lb 17/26 [58] fieldofsearch ..l74/11BH,12Bl-l,14Bl-l,15Bl-l, 174/16RH, 18, 31 R, 142, 152 R, DIG. 10

[56] References Cited UNITED STATES PATENTS 3,239,599 3/1966 Linderholm..174/18 X V 7 Feb. 15,1972

FOREIGN PATENTS OR APPLICATIONS 21,135 9/1968 Japan ..l74/15 BH PrimaryExaminer-Laramie E. Askin Attorney-Ostrolenk, Faber, Gerb & Soffen [5 7]ABSTRACT The grounded enclosure tube of the compressed-gas-insulatedelectrical conductor is attached to the metal wall of a powertransformer tank and the energized conductor tube extends into theinterior of the transformer tank wherein it is supported and insulatedfrom the tank wall to provide a simple and inexpensive connectionbetween metal enclosed switchgear, for example, and power transformersin a highvoltage electrical substation.

7 Claims, 2 Drawing Figures PATENIEI) FEB 1 5 I972 I N VENTOR.

flan 440 warm 57a TRANSFORMER TERMINATION FOR METAL- ENCLOSED,COMPRESSED-GAS-INSULATEI) ELECTRICAL CONDUCTORS The present inventionrelates to compressed-gas-insulated electrical conductors and, moreparticularly, to a novel termination design for use in high-voltagesubstations in which conductors or buses and other principal componentsare housed in grounded metal enclosures, and in which the energizedparts are insulated from the enclosures by a compressed insulating gassuch as sulphur hexafluoride (SF-6). Such other principal components mayinclude circuit breakers, switches and the like, and features ofcompressed-gas-insulated conductor systems useful to the presentinvention are disclosed in pending application Ser. No. 809,889 filedMar. 24, I969, now US. Pat. No. 3,573,341 issued Apr. 6, 1971.Compressed-gas-insulated conductors are normally comprised ofmetal-enclosed high-voltage electrical conductors in which a metallicconductor, generally tubular, is centrally supported within a groundedmetal tube of larger diameter by means of a solid disc or cone-shapeinsulator. The metallic conductor is insulated from the enclosure tubeby means of a compressed-gas, such as sulphur hexafluoride (SF6), havinga high dielectric characteristic. Such electrical conductors may be usedas buses in electrical substations and generating stations, or fortransmission of electrical power over either short, intermediate or longdistances. These metal-enclosed high-voltage electrical conductors maybe buried underground or supported at some convenient height aboveground.

The principal advantage of compressed-gas-insulated buses in atransmission system, as compared with conventional open buses, is atremendous reduction in the space requirement which such multiphase bussystems occupy. Whereas extra high-voltage (EHV) buses of openconstruction in air normally require ground clearances of 8 to feet andphase spacing 15 to 25 feet, buses of the metal-enclosedcompressed-gas-type can be provided with ground clearances of as littleas 4 to 10 inches and phase spacings of as little as 24 to 42 inches forthe same voltage ratings. In addition thereto, thecompressed-gas-insulated bus having a grounded metal enclosure for eachphase offers greater reliability and safety, as compared withconventional, open EI-IV conductors.

In the few substations which have been constructed employingcompressed-gas insulated conductors, connection between metal enclosedswitchgear and electrical power transformers in the substation havebeen'made either by means of open conductors or by means of cable. Withthe open conductor type of arrangement, a pair of porcelain bushings areusually employed, a first bushing to bring the energized conductor outfrom the metal enclosure and a second bushing at the point where theenergized conductor enters the metal tank of the power transformer.Characteristic of this scheme is that much of the safety advantage andspace savings existing with the metal enclosed substation is reduced ifexposed, energized conductors are used to connect the switchgear to thetransformer. Such construction is also relatively expensive, as is theuse of the high voltage cable arrangement wherein two cable terminationsare required for each phase. Where the cable is oil filled, in addition,oil pressurization equipment is further required, and significantly addsto the overall cost.

It is an object of the present invention to provide a novel arrangementfor terminating the metal-enclosed compressedgas-insulated conductordirectly on the tank wall of the electrical power transformer, so as toeliminate the added costs associated with the above described openconductor and cable connection arrangements. 7

It is anotherobject of the invention to provide a manner of mountingdoughnut-type current transformers in the oil of the power transformerunit at such a location as to protect the apparatus against flashoverthrough the oil from the energized parts.

ventional wound-paper condenser type of bushing which is normally usedinside power transformer assemblies to distribute voltage stresses.

It is a further object of the invention to eliminate the con It is yetanother object of the invention to provide a hermetically sealedtermination to inhibit leakage of the insulating gas into thetransformer oil.

It is also an object of the present invention to provide a terminationarrangement whereby the compressed-gas-insulated conductor enters thetransformer tank through a sidewall rather than through a top cover, soas not to increase substation height. 7 I

These and other objects of the invention will be more fully understoodfrom a consideration of the following description taken in connectionwith the drawings in which:

FIG. 1A is a partially sectionalized view of one preferred arrangementfor terminating a metal-enclosed, compressed-gasinsulated conductor atthe tank wall of a power transformer according to the present invention;and

FIG. 1b is a top view of a portion of FIG. 1a looking in the directionof arrows lb-lb As will become clear hereinafter, the metal enclosuretube of the compressed gas conductor is secured tothe metal tank wall,while the conductor tube extends into the interior of the transformertank where it is supported and insulated from the tank wall by a hollowconical or tubular bushing of porcelain, epoxy, or other such insulatingmaterial.

DESCRIPTION OF THE INVENTION In general, it will be seen that thearrangement of the invention includes concentric aluminum conductor andenclosure tubes which horizontally enter a transformer tank wall severalfeet below the minimum oil level of the transformer. A conically taperedhollow porcelain bushing is employed to support both these tubes and toinsulate the one from the other at the same time. The enclosure tubeenters the transformer tank wall through an outwardly extendingcylindrical pocket, which provides the necessary space in which to mountcurrent transformers of the doughnut type inside the tank and under theoil. In this manner, the current transformers are shielded from possibleflashover from the energized high-voltage parts.

Hermetic sealing of the described system is employed by way of copperrings which are soldered to a metal glaze provided at the end of theporcelain bushing. The inner portions of these copper rings are solderedto the copper portion of explosion-bonded bi-metallic copper-aluminumrings. The alu minum portion of these bi-metal rings is then welded tothe aluminum enclosure tube at the large diameter end of the taperedbushing and to the aluminum conductor tube at the smaller end of thebushing construction.

A corona ring is provided atthe end of the aluminum enclosure tubeinside the bushing, and the transformer tank wall is arranged so as toprovide a ring of ground potential metal outside the porcelainbushing'Use of such rings prevents high concentration of dielectricstress in the immediate vicinity of the metal flange ring which iscemented to the large diameter end of the bushing. Both rings arepositioned some several inches towards the live end of the bushing, andare effective in reducing the dielectric stress in their vicinities. Atthe same time, these grounded metal rings raise the corona onset andflashover voltages of the bushing assembly to the point at which aninternal condenser bushing is no longer needed to of the porcelainconstruction.

DESCRIPTION OFTHE ARRANGEMENT OF THE DRAWING V In the partiallysectionalized view shown in FIG. 1a it will be understood that theenclosure tube and conductor tube enter the left-hand side oftransformer tank 101. The transformer tank wall is represented by thenotation l0, and is so formed at its left-hand edge to establish anoutwardly extending cylindrical shell having a flange 11 extendingoutwardly from the left-hand end of shell 105. The shell is generally ofsteel or stainless steel fabrication, and when the transformer tank isshipped, a bolted and gasketed cover (not shown) is posi tioned to closeoff the cylindrical opening. When ready for field installation, however,this cover is removed and the high voltage conductor tube 15 andgrounded enclosure tube 16 are inserted therethrough in accordance withthe invention. Although not shown, it will be understood that theopposite wall of the transformer tank is positioned well beyond theright-hand end of FIG. la perhaps 15 to 25 feet to the right of wall 10.As shown, the tank 101 is generally rectangular in shape and is filledwith oil at atmospheric pressure up to a few inches from the top of thetank. In the description that follows, it will be understood that thehigh-voltage bus 15 enters the sidewall of the transformer tank; but insome applications, this conductor may enter vertically through the topof the tank arrangement. The specific arrangement will, of course,depend on the general setup of the high-voltage substatiomthe type oftransformer employed, and other factors of physical constraint. In allcases, however, theentire porcelain bushing 13 will be understood to bepositioned beneath the surface of the oil.

As shown in the drawings, the high-voltage conductor 15 is the innertube which enters the left-hand wall of the transformer tank 101 andextends directly from the bus construction through the inside of thetransformer tank and the interior of porcelain bushing 13, to the metalcasting 14 located at the right-hand end of FIG. la. Casting 14 servesas a support for the bushing 13, and additionally serves as thehigh-voltage terminal of the transformer. If desired, suitable cables orbus bar may be run to this high-voltage casting terminal 14, and canserve to couple the high voltage winding of the transformer to theterminal by means of the tapped holes l4a-14d, as indicated in FIG. 1b.(In one construction of the transformer, its core and winding coils werelocated under the oil surface and a few feet from the high-voltageterminal.) A disc-shaped epoxy insulator 100 is shown in the drawing assupporting the tubular conductor 15 over the length of its run, of theorder of 7 to 8 feet. In one arrangement according to the invention,conductor tube 15 was fabricated of aluminum. Entry of such a conductor15 was made through the transformer tank wall substantiallyhorizontally, and at a distance some 22 inches below the minimum oillevel of the power transformer. Such conductor 15 was concentricallyarranged with the outer enclosure I tube 16 (also of aluminum) and wasinsulated therefrom by means of a compressed-gas such assulfurhexafluoride (SF-6) filling the hollow interior defined byconductors I and 16.

The porcelain bushing 13 is conical in construction, tapering from itslarge end at the left to its smaller end at the right. As previouslynoted, this bushing is used to support the conductor and to furtherinsulate it from the enclosue tube 16. One way of attaching thehigh-voltage terminal casting 14 to the smaller right-hand end of theconical porcelain bushing 13 is to employ a flange 17 cemented (as at106) to a roughened surface of the bushing 13, with the casting 14 thenbeing bolted to this flange 17 by fasteners l8, 19. The interior ofbushing 13 is also filled with SF-6 insulating gas at the same pressureas the remainder of the bus system, namely 22 p.s.i. A solder sealarrangement is also shown in which a metallic ring 20 is soldered to ametal glaze provided on the porcelain bushing 13 with the inner part ofthe metal ring 20 being soldered,

welded or otherwise hermetically sealed to the tubular conductor 15 atits right most end. One manner of accomplishing this is to solder copperrings to correspondingly positioned platinum rings fired into the glazeat the right end of porcelain bushing. The copper ring, in turn, may besoldered to the copper portion of an explosion-bonded bi-metalliccopper-' aluminum ring, with the aluminum ring being welded to thealuminum conductor tube 15 at the small end of the bushing.

. (An alternate method of securement would be to use gaskets between aground surface at the small end of the porcelain bushing 13 and a metalplate clamped against the ground surface of the porcelain bushing).

A second, larger diameter flange 21 is positioned at the lefthand end ofthe tapered bushing 13, and is electrically connected to groundpotential. The flange 21 is also cemented (as at 107) to the porcelainbushing 13, and a solder-seal arrangement similar to that at its rightend is effected-e.g., by welding the aluminum portion of copper-aluminumbi-metallic rings 22 to the aluminum enclosure tube 16.

Such construction thus effects a complete metallic hermetic seal betweenthe bushing 13 and the enclosure tube 16, which in one embodiment of theinvention, had an outer diameterof 18 inches. Although gasketedconstruction could be used to provide the hermetic seal, in the manneroutlined above, such construction has the disadvantage that leak proofservice over many years may not remain percent effective. While loss ofthe SF-6 gas into the oil would not be particularly harmful, such gaswould have to be replenished in an operation which could becomeexpensive if the leak were sizable. No deleterious operation of theequipment would result, however, since the SF6 gas is itself a goodinsulating medium and secondly because it would have a tendency to riseto the top of the insulating oil surface. I v

The current transformer 24 employed in the construction of the drawingmay be of the doughnut" or toroidal type. The current transformer 24consists of a ring-shaped core which is made up of many thinlaminations, having many turns of insulated wire wound in a toroidalmanner around the core. Current transformers having ratings such as3,000/5, 2,000/5 and 1,200/5 may be used with the invention.

The porcelain bushing 13 in one embodiment of the invention had a lengthof some 4 feet and tapered over this length from a diameter of some 26inches or so to a diameter approximately 10 inches. The weight of such abushing was supported entirely from the large clamp 25 shown bolted tothe flange 21 at the large end of the bushing 13, which clamp-isin turnfurther clamped (as at 26) and finally welded (at 27) to the exterior ofthe enclosure tube 16. The current transformers 24 are selected to havean inner diameternot less than 18 to 19 inches and'an outer diameter notmore than 33 to 34 inches. The preferred arrangement as thus fardescribed may be located a height of 14 feet or so above ground.

It has been found that a high concentration of dielectric stress maybeestablished in the immediate vicinity of the flange 21 cemented to thelarge diameter end of the bushing 13. To reduce this concentration, acorona ring 28 is provided at the endof the enclosure tube 16 inside thebushing 13 and the transformer tank 101 is grounded. The presence ofthis grounded transformer tank together with the corona ring combine togive a fairly uniform field in this location and raise both the coronaonset and flashover voltage of the bushing as sembly to a levelsufficient to avoid the need for an internal condenser bushing which isconventionally employed to provide uniform voltage distribution alongthe surface of the bushing. It canbe seen that the corona ring 28 isextended several inches (for example 7 inches) to the right of theflange 21 so as to provide a ring of ground potential metal outside theporcelain.

A ribbed aluminum casting 29 is further shown at the left hand end ofFIG. 1a as surrounding the enclosure tube 16 so as to support the entireassembly of the transformer conductor-bushing arrangement. In order thatthe support also be oil tight, it is preferable to weld the casting tothe enclosure tube as shown at 30 and to use a gasket 31 around theouter periphery of the casting to prevent oil leakage at this point.Since the oil is at atmospheric pressure, leakage prevention at thesepoints is not particularly difficult.

Also shown in the drawing are a number of phenolic washers 32 used insecuring the porcelain bushing 13 to the enclosure tube 16. The functionof these washers is to help support the rather heavy weight of theporcelain bushing, which for the size set forth hereinabove, weighsabout 500 pounds. These washers are selected of insulating materialrather than metal because the current flowing in the conductor 15 tendsto induce a voltage in the enclosure tube 16 which tries to establish acurrent of equal magnitude in the enclosure tube 16, but in an oppositedirection to the current flowing in the conductor 15. If such werepermitted to occur, the current transformers 24 would not read correctlyin that they would essentially detect only the difference in the twocurrents; if a good metallic connection were made at this point, thecurrent transformers employed would read almost zero current flowing inthe main conductor, whereas the fact may be that a current of 3,000amperes flows towards the right in the conductor but is cancelled by anequal current of 3,000 amperes flowing in the opposite direction in theenclosure tube 16. Since the current transformer 24 surrounds bothconductor 15 and enclosure 16, it would read only the net currentflowing through the hole of the doughnut" and would therefore beunsatisfactory as a current measuring device.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appending claims.

I claim:

1. in combination, a high-voltage oil-filled transformer tank having anopening in one wall of the tank;

a gas filled insulated bus comprising a tubular inner conductorsurrounded by a concentric conductive tubular housmg;

one end of said inner conductor extending into said tank;

one end of said tubular housing terminating in the region adjacent saidopening;

first means securing said tubular housing to said tank wall including aconical shaped power transformer insulator bushing surrounding saidtubular conductor, the large diameter end of said bushing being securedto the tank adjacent said opening;

second means securing the small diameter end of said bushing to said oneend of said tubular conductor;

a cylindrical shell extending outwardly from said tank wall opening andsurrounding a portion of said tubular housing;

third and fourth means respectively sealing the junctures between saidbushing and said tank and between said bushing and said tubularconductor to prevent gas from said bus entering into the interior ofsaid bushing from leaking into said tank, means mechanically securingsaid tubular housing to said cylindrical shell.

2. The combination of claim 1 further comprising toroidal shapedtransformer means positioned within said cylindrical shell andsurrounding said tubular housing.

3. The combination of claim 2 wherein said first means further includesmeans insulating said one end of said tubular housing from saidcylindrical shell.

4. The combination of claim 1 wherein said one end of said tubularhousing is provided with a corona ring to eliminate high voltagegradients at the adjacent end of said bushing.

5. The combination of claim 1 wherein said third and fourth means eachcomprise weldments respectively joining the bushing ends to said tubularconductor and said tubular housmg.

6. The combination of claim 1 wherein said bushing is provided withmetallic surfaces at each end thereof;

said first means being comprised of a metallic ring respectively weldedto said tubular housing and one of said metallic surfaces;

said second means being comprised of a metallic ring respectively weldedto said conductor and one of said metallic surfaces.

7. The combination of claim 6 wherein said metallic rings are eachcomprised of explosion bonded bimetallic aluminum copper rings;

said mechanical securing means comprising a clamping assembly securingsaid tubular housing to the interior of said cylindrical shell;

fifth means sealing the free end of said cylindrical shell to saidtubular housing a spaced distance from said one end of said tubularhousing.

1. In combination, a high-voltage oil-filled transformer tank having anopening in one wall of the tank; a gas filled insulated bus comprising atubular inner conductor surrounded by a concentric conductive tubularhousing; one end of said inner conductor extending into said tank; oneend of said tubular housing terminating in the region adjacent saidopening; first means securing said tubular housing to said tank wallincluding a conical shaped power transformer insulator bushingsurrounding said tubular conductor, the large diameTer end of saidbushing being secured to the tank adjacent said opening; second meanssecuring the small diameter end of said bushing to said one end of saidtubular conductor; a cylindrical shell extending outwardly from saidtank wall opening and surrounding a portion of said tubular housing;third and fourth means respectively sealing the junctures between saidbushing and said tank and between said bushing and said tubularconductor to prevent gas from said bus entering into the interior ofsaid bushing from leaking into said tank, means mechanically securingsaid tubular housing to said cylindrical shell.
 2. The combination ofclaim 1 further comprising toroidal shaped transformer means positionedwithin said cylindrical shell and surrounding said tubular housing. 3.The combination of claim 2 wherein said first means further includesmeans insulating said one end of said tubular housing from saidcylindrical shell.
 4. The combination of claim 1 wherein said one end ofsaid tubular housing is provided with a corona ring to eliminate highvoltage gradients at the adjacent end of said bushing.
 5. Thecombination of claim 1 wherein said third and fourth means each compriseweldments respectively joining the bushing ends to said tubularconductor and said tubular housing.
 6. The combination of claim 1wherein said bushing is provided with metallic surfaces at each endthereof; said first means being comprised of a metallic ringrespectively welded to said tubular housing and one of said metallicsurfaces; said second means being comprised of a metallic ringrespectively welded to said conductor and one of said metallic surfaces.7. The combination of claim 6 wherein said metallic rings are eachcomprised of explosion bonded bimetallic aluminum copper rings; saidmechanical securing means comprising a clamping assembly securing saidtubular housing to the interior of said cylindrical shell; fifth meanssealing the free end of said cylindrical shell to said tubular housing aspaced distance from said one end of said tubular housing.